前言
说到iOS自动布局，有很多的解决办法。有的人使用xib/storyboard自动布局，也有人使用frame来适配。对于前者，笔者并不喜欢，也不支持。对于后者，更是麻烦，到处计算高度、宽度等，千万大量代码的冗余，对维护和开发的效率都很低。
笔者在这里介绍纯代码自动布局的第三方库：Masonry。这个库使用率相当高，在全世界都有大量的开发者在使用，其star数量也是相当高的。
效果图
本节详解Masonry的循环创建视图，并且可以展开与收缩的用法，先看看效果图：
当我们点击某一行时，可以展开：
核心代码
看下代码：
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@interface ScrollViewComplexController ()
@property (nonatomic, strong) UIScrollView *scrollView;
@property (nonatomic, strong) NSMutableArray *expandStates;
@end
@implementation ScrollViewComplexController
- (void)viewDidLoad {
[super viewDidLoad];
self.scrollView = [[UIScrollView alloc] init];
self.scrollView.pagingEnabled = NO;
[self.view addSubview:self.scrollView];
self.scrollView.backgroundColor = [UIColor lightGrayColor];
CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
UILabel *lastLabel = nil;
for (NSUInteger i = 0; i < 10; ++i) {
UILabel *label = [[UILabel alloc] init];
label.numberOfLines = 0;
label.layer.borderColor = [UIColor greenColor].CGColor;
label.layer.borderWidth = 2.0;
label.text = [self randomText];
label.userInteractionEnabled = YES;
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap:)];
[label addGestureRecognizer:tap];
// We must preferredMaxLayoutWidth property for adapting to iOS6.0
label.preferredMaxLayoutWidth = screenWidth - 30;
label.textAlignment = NSTextAlignmentLeft;
label.textColor = [self randomColor];
[self.scrollView addSubview:label];
[label mas_makeConstraints:^(MASConstraintMaker *make) {
make.left.mas_equalTo(15);
make.right.mas_equalTo(self.view).offset(-15);
if (lastLabel) {
make.top.mas_equalTo(lastLabel.mas_bottom).offset(20);
} else {
make.top.mas_equalTo(self.scrollView).offset(20);
}
make.height.mas_equalTo(40);
}];
lastLabel = label;
[self.expandStates addObject:[@[label, @(NO)] mutableCopy]];
}
[self.scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
make.edges.mas_equalTo(self.view);
// 让scrollview的contentSize随着内容的增多而变化
make.bottom.mas_equalTo(lastLabel.mas_bottom).offset(20);
}];
}
- (NSMutableArray *)expandStates {
if (_expandStates == nil) {
_expandStates = [[NSMutableArray alloc] init];
}
return _expandStates;
}
- (UIColor *)randomColor {
CGFloat hue = ( arc4random() % 256 / 256.0 ); // 0.0 to 1.0
CGFloat saturation = ( arc4random() % 128 / 256.0 ) + 0.5; // 0.5 to 1.0, away from white
CGFloat brightness = ( arc4random() % 128 / 256.0 ) + 0.5; // 0.5 to 1.0, away from black
return [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];
}
- (NSString *)randomText {
CGFloat length = arc4random() % 150 + 5;
NSMutableString *str = [[NSMutableString alloc] init];
for (NSUInteger i = 0; i < length; ++i) {
[str appendString:@"测试数据很长，"];
}
return str;
}
- (void)onTap:(UITapGestureRecognizer *)sender {
UIView *tapView = sender.view;
NSUInteger index = 0;
for (NSMutableArray *array in self.expandStates) {
UILabel *view = [array firstObject];
if (view == tapView) {
NSNumber *state = [array lastObject];
if ([state boolValue] == YES) {
[view mas_updateConstraints:^(MASConstraintMaker *make) {
make.height.mas_equalTo(40);
}];
} else {
UIView *preView = nil;
UIView *nextView = nil;
if (index - 1 < self.expandStates.count && index >= 1) {
preView = [[self.expandStates objectAtIndex:index - 1] firstObject];
}
if (index + 1 < self.expandStates.count) {
nextView = [[self.expandStates objectAtIndex:index + 1] firstObject];
}
[view mas_remakeConstraints:^(MASConstraintMaker *make) {
if (preView) {
make.top.mas_equalTo(preView.mas_bottom).offset(20);
} else {
make.top.mas_equalTo(20);
}
make.left.mas_equalTo(15);
make.right.mas_equalTo(self.view).offset(-15);
}];
if (nextView) {
[nextView mas_updateConstraints:^(MASConstraintMaker *make) {
make.top.mas_equalTo(view.mas_bottom).offset(20);
}];
}
}
[array replaceObjectAtIndex:1 withObject:@(!state.boolValue)];
[self.view setNeedsUpdateConstraints];
[self.view updateConstraintsIfNeeded];
[UIView animateWithDuration:0.35 animations:^{
[self.view layoutIfNeeded];
} completion:^(BOOL finished) {
}];
break;
}
index++;
}
}
@end
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讲解
当我们要收起的时候，只是简单地设置其高度的约束为40，但是当我们要展开时，实现起来就相对麻烦了。因为我们需要重新添加约束，要重新给所点击的视图添加约束，就需要知道前一个依赖视图和后一个依赖视图的约束，以便将相关联的都更新约束。
当我们更新所点击的视图时，我们通过判断是否有前一个依赖视图来设置顶部约束：
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if (preView) {
make.top.mas_equalTo(preView.mas_bottom).offset(20);
} else {
make.top.mas_equalTo(20);
}
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除了这个之外，我们也需要更新后一个视图的约束，因为我们对所点击的视图调用了mas_remakeConstraints方法，就会移除其之前所添加的所有约束，所以我们必须重新将后者对当前点击的视图的依赖重新添加上去：
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if (nextView) {
[nextView mas_updateConstraints:^(MASConstraintMaker *make) {
make.top.mas_equalTo(view.mas_bottom).offset(20);
}];
}
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